Dark Suns is a setting that is wildly different than traditional fantasy, great for adventures where the odds are not at all stacked towards heroes. I cannot recommend it for new players due to the generally intense difficulty (especially for good aligned characters), but for veterans who understand the mechanics and want something shying away from traditional fantasy but is still DnD, this is a good choice. The setting essentially rewrites traditional lore, most of the old (standard anyways) playable races are detailed but very different both culturally and mechanically. Additionally new races are introduced such as the thri-kreen and half-giants. While some old classes are still playable, vanilla Dark Suns does not allow several (such as the Paladin) and others are different mechanically (such as clerics and spellcasters). New classes are also added, including the Templar, a class where the character is required to have an evil alignment (unusual for a traditional player). For anyone who knows little of the setting, read the lore and mechanics book thoroughly, some things are quite surprising (such as how "potions" work, or how old races function in this setting). My one gripe is the lack of material on how Sorcerer Kings operate. They are the incredibly powerful kings of the various city states, but only vague lore and virtually no mechanics are given for their operation, making it difficult to run new worlds based on the Dark Sun traditional world, or even to simply run extremely high level campaigns. For that I suggest the Dragon Kings supplement, which provides material for characters and NPCs above level 20 (and included lore and mechanics for the "Dragon Kings" or Sorcerer Kings).